Steam generator

ABSTRACT

A steam generator is disclosed for application to nuclear reactors having a U-tube heat exchanger for carrying a primary and a secondary heating medium. In accordance with the invention, a portion of the secondary heating medium is uniformly distributed into the generator in the region of the separators by distributing the medium over the separator cross section. By introducing the secondary medium in this manner, the circulating water is thereby cooled and the steam contained in it is condensed. The formation of bubbles or foam which make the control of the water level in the steam generator difficult and which cause oscillations in the circulation of the steam generator are thus largely avoided.

United States Patent [1 1 Mayer et al.

[ Dec. 17, 1974 STEAM GENERATOR [75] inventors: Hans Mayer; Heinz-Jurgen Schroder; Gerhard Schucktanz, Erlangen, all of Germany [73] Assignee: Siemens Aktiengesellschaft, Munich,

Germany [22] Filed: Nov. 15, 1972 [21] Appl. No.: 306,939

[30] Foreign Application Priority Data Nov. 17, 1971 Germany 2157069 [52] US. Cl 122/32, 122/34, 122/491 [51] Int. Cl. F22b l/06 [58] Field of Search 122/32, 33, 34, 491

[56] References Cited UNITED STATES PATENTS 3,250.258 5/1966 Hcathcote v. 122/34 3,296,779 1/1967 Daman ct al. 122/34 X 3,682,140 8/1972 Roffler 122/34 Primary Examiner-Kenneth W. Sprziguc Attorney, Agent, or Firm-Kenyon & Kenyon Reilly Carr & Chapin [57] ABSTRACT A steam generator is disclosed for application to nuclear reactors having a U-tube heat exchanger for carrying a primary 'and a secondary heating medium. in accordance with the invention, a portion of the secondary heating medium is uniformly distributed into the generator in the region of the separators by distributing the medium over the separator cross section. By introducing the secondary medium in this manner, the circulating water is thereby cooled and the steam contained in it is condensed. The formation of bubbles or foam which make the control of the water level in the steam generator difficult and which cause oscillations in the circulation of the steam generator are thus largely avoided.

4 Claims, 5 Drawing Figures PATENTELBEBWQM 3.854.453 SHEET 2 BF 3 STEAM GENERATOR FIELD OF THE INVENTION This invention is concerned with steam generators, particularly with steam generators used in nuclear reactors in which a heat exchanger is used for carrying a primary and a secondary heating medium and in which separators are located above the heat exchangers.

DESCRIPTION OF THE PRIOR ART Steam generators of the type described above have been disclosed, for example, in the book Betrieb von Kernkraftwerken (Operation of Nuclear Power Plants), vol. 37, Verlag Kiemig Muenchen, 1969, p. 18-20. In these steam generators, the input of the feed water takes place in a region below the separators. Thus, the mixing of the circulating water with the input water also occurs in this area. Because the circulating water also contains a steam component commonly referred to as carry-under, the system has inherent disadvantages with respect to the control of the water level and the stability of the evaporation system. The formation of bubbles and foam in the steam generator produces an indeterminate rise in the water level which leads to difficulties in the control of the water level. This effects the efficiency of the separators and their ability to precipitate water resulting in an increase in the moisture content in the steam. Because of bubble formation, oscillations may be excited in the circulation of the steam generator resulting in unstable operating conditions. Because the circulating water contains a steam component (the ratio of the steam volume to the water volume is approximately 30:1), the overall return volume is increased. Further the velocity of the inflowing water in the cross sectional area of the steam generator circulating system is also increased, intensifying the foam formation and further uncontrollably increasing the water level. The problem is thus to prevent the formation of as little steam in the circulating water as possible.

SUMMARY OF THE INVENTION According to the invention, these problems are solved by uniformly feeding at least a portion of the secondary medium into the cross sectional area of the separators.

By feeding the secondary heating medium or the feed water, in proximity to the separators, the circulating water which is guided by the separators and is mixed with steam, is cooled and the steam component carried along therewith is condensed. Bubble or foam formation therefore does not occur, and substantially better control of the water level in the steam generator as well as favorable stability behavior are achieved.

In order to obtain the most uniform distribution possible of the secondary medium fed in proximity to the separators, the secondary medium can be fed in by a distributor plate. Alternatively, pipe lines having several discharge openings can be provided to introduce secondary medium in the region of the separators, where the pipe lines may be arranged in star fashion running toward the center of the steam generator.

BRIEF DESCRIPTION OF THE DRAWINGS The objectives and advantages of the apparatus of this invention will become more readily apparent to those skilled in the art from the following detailed description taken in conjunccion with the accompanying drawings of which:

FIG. 1 is a longitudinal cross-sectional view of the steam generator;

FIG. 2 is a horizontal cross-sectional view of the generator taken along lines IIII of FIG. 1;

' FIG. 3 is a partial longitudinal cross-sectional view of a modified feeding system;

FIG. 4 is a partial longitudinal cross-sectional view of a modified feeding system; and

FIG. 5 is a partial longitudinal cross-sectional view of a modified feeding system.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIG. 1 which is a longitudinal crosssectional view through a steam generator, the previously known U-tube heat exchanger 2 has a primary heating medium inlet 3 and the primary heating medium outlet 4 within a tank enclosure 1. A separator 5 is located above the group of U-tubes 2. Any steam generated within the system flows out through the livesteam output line 6 in steam dome 7. The cold secondary medium is fed in by an inlet 8 and flows from ring pipe 9, situated below water level 10, into ring gap 11 between the cylindrical baffle 12 and the tank enclosure 1. The cylindrical baffle l2 surrounds the group of U-tubes 2 and serves as the support for separator 5. The secondary heating medium flowing downward in ring gap 11, enters the group of tubes 2 through openings 14 directly above tube plate 13. The secondary heating medium rises in the U-tubes 2, forming'steam bubbles. The generated steam flows out through the output line 6. The circulating water flows off separator 5 into ring gap 11, mixing with the freshly fed secondary heating medium from ring line 9.

In the known steam generator of the type described so far, having natural circulation, the circulating water running off from separator 5 has a large steam content. The disadvantages of this type of device have already been described. For the purpose of cooling the circulating water carried away from the separators and mixed with the water carried away with it, several pipe line systems 15 are provided in the embodiment illustrated in FIG. 1. These pipe line systems run out from ring line 9 to the region of the separator 5 and are installed between the individual elements of the separator. The pipe lines 15 are provided with several discharge openings 15a, through which the feed water flows to the region of the separator 5, and is distributed as uniformly as possible. By this means sufficient mixing of the circulating water with the feed water, in the proximity of the separator, is assured. Through the uniform cooling of the circulating water in the separation zone, the steam component is condensed and bubble or foam formation is avoided.

From FIG. 2, which shows a cross-sectional view along lines IIII of FIG. 1, several pipe lines 15 are led in star fashion from the ring line 9 to the region of the separator 5. (Separator 5 is not included in FIG. 2 in order to maintain simplicity.) By means of the dis-- charge openings 15a in pipes 15, the uniform feeding of the secondary heating medium in the area of the separator 5 is achieved. Accordingly, uniform cooling of the circulating water is obtained.

In the description of the steam generator shown in FIG. 1 it was presumed that a portion of the secondary heating medium is fed directly into the ring gap 11 by ring line 9. This type of feeding however is not necessary, and the entire secondary medium can be fed in through pipe lines 15.

FIG. 3 illustrates a different embodiment of the feeding system. In FIG. 3 pipe lines 15 are not brought directly into proximity with separator 5, but pipe lines 15 run, for example, in star fashion above separator and are provided with downward extending pipes 16, reaching between the separator elements. The secondary medium emerges within separator 5 from the pipe openings at the end of pipes 16 and additionally from discharge openings 16a. In this embodiment the feed lines for the secondary medium thus end above the circulating water outlet 17 of the separator elements of separator 5. The uniform cooling of the circulating water thus is not impaired.

In the feeding system illustrated in FIG. 4, pipe lines also run in star fashion between the elements of separator 5, below exit plane 17 of the circulating water from separator 5. In this embodiment, however, the pipe system 15 is not fed from a ring line, but the secondary medium is fed to it centrally through the feed inlet 18. In this embodiment one achieves the advantage that the diameter of the tank enclosure 1 can be reduced, leading to considerable cost savings.

In the embodiment shown in FIG. 5, a distributor plate 19 is provided to feed in the secondary medium. This distributor plate 19 acts as a double plate replacing the otherwise customary plate on which the elements of separator 5 are mounted. The inlet pipes for the elements of the separator penetrate the double plated sandwich construction. The feed water is conducted through the feed line 20 into the distributor plate 19 and flows from there uniformly over the separator cross section through discharge openings and then upward between the inlet pipes of separator 5 and into proximity with separators 5. As in the previously described embodiments, the secondary medium is mixed with the circulating water flowing from the elements of separator 5. Because the discharge openings for the feed water can be distributed extremely uniformly in the upper plate of distributor plate 19, a particularly uniform mixing of the circulating water with the feed water is obtained by this embodiment.

A possible alternative, is a feed line 20a, shown in FIG. 5 by dotted lines. By feed line 20a feed water is fed into the distributor plate 19 from the top through the elements of separator 5. This feed line 200 can be connected to the distributor plate 19 at any point on its cross section.

In summary, it can be stated that a definite, controllable water level can be obtained by the steam generator of this invention, because the formation of foam in the circulating water is prevented. The amount of residual moisture remaining in the live steam is eliminated and the capacity of the separators increased. The number of separator elements required can therefore be reduced, resulting in considerable cost savings. Furthermore, the cross-sectional flow-off area for the circulating water can be made smaller, making it possible to reduce the diameter of the tank enclosure in the steam generator, resulting in additional cost savings. Further, the risk of instability in the circulation system is reduced and by the steam generator manufactured according to the invention a greater increase in secondary pressure is possible, because the carry-under, which increases with increasing secondary pressure, is condensed.

In the foregoing, the invention has been described in reference to specific exemplary embodiments. It will be evident however, that variations and modifications, as well as the substitution of equivalent constructions and arrangements for those shown for illustration, may be made without departing from the broader scope and spirit of the invention as set forth in the appended claims. The specification and drawings are accordingly to be regarded in an illustrative rather than in a restrictive sense.

What is claimed is:

l. A steam generator having a steam dome with a steam output line in its upper portion and a tank enclosure below said dome, a heat exchanger in said enclosure, a water separator in said steam dome and dis charging water downwardly, and a feed-water inlet for said tank; wherein the improvement comprises means for distributing at least a portion of the feed-water from said inlet throughout the cross-sectional area of said separator.

2. The steam generator of claim 1 in which within said tank enclosure said heat exchanger is surrounded by an annular baffle forming an annular space between it and said tank enclosure, having a lower portion opening to a lower portion of said exchanger and an upper portion to which said separator is connected above said exchanger, said separator discharging a plurality of streams of separated feed-water for descent downwardly through said space and from the lower portion of said baffle said water rising within said baffle and mixed with steam going through said separator, an annular pipe in the upper portion of said space adjacent to said separator being connected to said feed-water inlet, said means being formed by a feed-water conductor connected to said annular pipe and forming a plurality of feed-water outlets positioned directly in said streams discharged by said separator.

3. The steam generator of claim 2 in which said conductor is in the form ofa hollow plate having a plurality of outlets distributed transversely throughout said separator.

4. The steam generator of claim 2 in which said conductor is in the form of a plurality of pipes extending radially inwardly from said annular pipe into said separator towards its center in star fashion. 

1. A steam generator having a Steam dome with a steam output line in its upper portion and a tank enclosure below said dome, a heat exchanger in said enclosure, a water separator in said steam dome and discharging water downwardly, and a feed-water inlet for said tank; wherein the improvement comprises means for distributing at least a portion of the feed-water from said inlet throughout the cross-sectional area of said separator.
 2. The steam generator of claim 1 in which within said tank enclosure said heat exchanger is surrounded by an annular baffle forming an annular space between it and said tank enclosure, having a lower portion opening to a lower portion of said exchanger and an upper portion to which said separator is connected above said exchanger, said separator discharging a plurality of streams of separated feed-water for descent downwardly through said space and from the lower portion of said baffle said water rising within said baffle and mixed with steam going through said separator, an annular pipe in the upper portion of said space adjacent to said separator being connected to said feed-water inlet, said means being formed by a feed-water conductor connected to said annular pipe and forming a plurality of feed-water outlets positioned directly in said streams discharged by said separator.
 3. The steam generator of claim 2 in which said conductor is in the form of a hollow plate having a plurality of outlets distributed transversely throughout said separator.
 4. The steam generator of claim 2 in which said conductor is in the form of a plurality of pipes extending radially inwardly from said annular pipe into said separator towards its center in star fashion. 